Family Xyridaceae

Xyridaceae C.A. Agardh

Including Abolbodaceae Nak.

Habit and leaf form. Herbs. Perennial; with a basal aggregation of leaves; rhizomatous. Helophytic, or mesophytic, or xerophytic. Leaves alternate; spiral (Abolbodaceae), or distichous (mostly); flat, or terete; ‘herbaceous’, or leathery; sessile; sheathing. Leaf sheaths with free margins. Leaves edgewise to the stem, or with ‘normal’ orientation; simple. Lamina entire; linear; parallel-veined; without cross-venules. Leaves ligulate, or eligulate.

General anatomy. Plants without silica bodies. Accumulated starch other than exclusively ‘pteridophyte type’.

Leaf anatomy. Stomata present; paracytic.

The mesophyll not containing mucilage cells; containing calcium oxalate crystals, or without calcium oxalate crystals. The mesophyll crystals druses, or solitary-prismatic (i.e. no raphides). Vessels present; end-walls simple.

Stem anatomy. Secondary thickening absent. Xylem with vessels. Vessel end-walls simple.

Root anatomy. Root xylem with vessels; vessel end-walls simple.

Reproductive type, pollination. Unisexual flowers absent. Plants hermaphrodite. Floral nectaries absent (nectaries lacking). Pollination entomophilous.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in spikes and in heads. The ultimate inflorescence unit racemose. Inflorescences scapiflorous; usually a simple, headlike spike, rarely more than one spike; with involucral bracts, or without involucral bracts; pseudanthial, or not pseudanthial. Flowers bracteate; ebracteolate; small, or medium-sized; regular to very irregular; when irregular, zygomorphic. The floral irregularity involving the perianth, or involving the perianth and involving the androecium. Flowers 3 merous; cyclic; tetracyclic, or pentacyclic. Perigone tube absent. Hypogynous disk absent.

Perianth with distinct calyx and corolla; 6; free, or free and joined; 2 whorled; isomerous, or anisomerous; different in the two whorls. Calyx (2–)3 (the median member sometimes lacking — or caducous?); 1 whorled; polysepalous, or partially gamosepalous. Sometimes having 2 of the members joined (the laterals, basally). Calyx unequal but not bilabiate; persistent. Corolla 3; 1 whorled; polypetalous, or gamopetalous (Abolbodaceae); imbricate; unequal but not bilabiate; yellow (usually), or white, or blue. Petals when free clawed, or sessile (?).

Androecium 3, or 6. Androecial members adnate; free of one another; 1 whorled, or 2 whorled. Androecium exclusively of fertile stamens (Abolbodaceae, representing the inner whorl), or including staminodes. Staminodes when present, 3 (the outer whorl); external to the fertile stamens; non-petaloid (sometimes plumose-branched). Stamens 3; isomerous with the perianth; oppositiperianthial. Anthers dehiscing via longitudinal slits; latrorse; tetrasporangiate. Endothecium not developing fibrous thickenings. Anther epidermis persistent. Microsporogenesis successive. The initial microspore tetrads isobilateral, or decussate. Anther wall initially with one middle layer. Tapetum amoeboid, or glandular. Pollen shed as single grains. Pollen grains aperturate (Xyris), or nonaperturate; when aperturate, 1 aperturate, or 2 aperturate; sulcate, or sulculate; psilate to muricate (?), or spinulose (Abolbodaceae); 2-celled.

Gynoecium 3 carpelled. Carpels isomerous with the perianth. The pistil 1 celled, or 3 celled. Gynoecium syncarpous; synstylovarious to eu-syncarpous; superior. Ovary 1 locular, or 3 locular (or incompletely trilocular). Gynoecium stylate. Styles 1 (three-branched); apical. Stigmas 1, or 3. Placentation when unilocular, parietal, or basal; when trilocular, axile. Ovules in the single cavity when unilocular, 1–100 (to ‘many’); 1–50 per locule (to ‘many’); non-arillate; orthotropous, or anatropous to campylotropous; bitegmic; tenuinucellate. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed, or not formed (then the three nuclei degenerating early); when formed, 3; not proliferating; ephemeral. Synergids sometimes shortly hooked. Endosperm formation nuclear, or helobial.

Fruit non-fleshy; dehiscent; a capsule. Capsules loculicidal, or circumscissile. Seeds endospermic. Endosperm oily, or not oily. Seeds winged, or wingless. Embryo rudimentary at the time of seed release to weakly differentiated (small to large). Cotyledons 1 (bifacial). Embryo straight to curved (large and curved in Abolbodaceae). Testa without phytomelan.

Seedling. Hypocotyl internode present (short, with rhizoids). Seedling collar not conspicuous. Cotyledon hyperphyll elongated; assimilatory; dorsiventrally flattened. Coleoptile absent. Seedling cataphylls present. First leaf ensiform. Primary root ephemeral.

Physiology, biochemistry. Alkaloids absent (2 species). Proanthocyanidins at least sometimes present; cyanidin. Flavonols absent. Ellagic acid absent. Saponins/sapogenins sometimes present. Aluminium accumulation demonstrated.

Geography, cytology. Mainly sub-tropical and tropical. North and South America, Asia, Africa and Australia. X = 9, 13, 17 (all counts for Xyris).

Taxonomy. Subclass Monocotyledonae. Dahlgren et al. Superorder Commeliniflorae; Commelinales. APG 3 core angiosperms; Superorder Lilianae; commelinid Monocot; Order Poales.

Species about 270. Genera 5; Abolboda, Achlyphila, Aratitiyopea, Orectanthe, Xyris.

Economic uses, etc. Xyris supplies watergarden and aquarium ornamentals.

Illustrations.
• Technical details: Xyris (Thonner).
• Technical details: Xyris (Lindley).